Following a couple simple steps can take away some of the guesswork:
MEASURE YOUR DOG'S NECK - The easiest way to measure is to use a sewing or tailor's tape. If you don't have that type of measuring tape, your dog's old collar, a shoestring, or even a dog leash can be used to wrap around the dog's neck and get a length...by measuring that length with a tape measure or a ruler, you will come up with a good neck measurement. Be sure to consider the dog's fur, and leave enough room for a couple fingers under the collar.
ORDER A COLLAR BASED ON THE MEASUREMENT - Using our size drop-down menu, pick the collar size that is closest to your dog's neck measurement. If your dog's neck measurement falls on a crossover size (for example 18"...our Medium is 12"-18" and Large is 18"-26"), decide if you want to be able to adjust smaller or larger than the measurement and pick the size accordingly.
PRO TIP: If your dog's neck measurement falls on a crossover size (like 18-inches, which is the top end of the Medium collar and the bottom end of the Large collar), you'll need to make a judgement call. Which way would you like the ability to adjust? Is your dog growing? If you think 18" may be a bit tight, go for the Large.